Somehow (I suspect your mirror is out of date) you are using an old version of ubuntu-release-upgrader, the bug you are encounter (DEBUG blacklist expr 'unity$' matches 'unity') was fixed in ubuntu-release-upgrader version 18.04.18.
Somehow (I suspect your mirror is out of date) you are using an old version of ubuntu- release- upgrader, the bug you are encounter (DEBUG blacklist expr 'unity$' matches 'unity') was fixed in ubuntu- release- upgrader version 18.04.18.